Conventionally, for example, a solid high-polymer membrane-type fuel cell is provided with a cell wherein a solid high-polymer electrolytic membrane is sandwiched between a fuel electrode and an oxygen electrode, and a plurality of cells are configured in a layered stack (hereafter referred to as a fuel cell). Hydrogen is supplied to the fuel electrode as fuel, and air is supplied to the oxygen electrode as oxidant, and oxygen ions produced at the fuel electrode due to a catalytic reaction pass through the solid high-polymer electrolytic membrane and migrate to the oxygen electrode, so that electricity is generated by an electrochemical reaction with oxygen at the oxygen electrode.
In fuel cells such as this solid high-polymer membrane-type fuel cell, conventionally there is known a protective apparatus which is provided with a hydrogen detector (gas sensor) in the exhaust system, for example on the oxygen electrode side of the fuel cell, and if this hydrogen detector detects leakage of hydrogen from the fuel electrode through the solid high-polymer electrolytic membrane to the oxygen electrode, it shuts off the supply of fuel (refer for example to Japanese Unexamined Patent Application, First Publication No. H06-223850).
Furthermore, as the hydrogen detector there is known a gas-contact combustion-type hydrogen detector which is provided with a gas detection element including for example a catalyst of platinum or the like, and a temperature compensation element as a pair. This hydrogen detector detects the concentration of hydrogen gas according to a difference in electrical resistance which occurs between a condition of the temperature compensation element for when the gas detection element becomes relatively hot due to heat produced by combustion when hydrogen contacts the catalyst of platinum or the like, and a condition at a relatively low temperature such as under ambient temperature.
Incidentally, in the fuel cell of the solid high-polymer membrane-type fuel cell and the like as described above, in order to maintain the ion conductivity of the solid high-polymer electrolytic membrane, water (humidifying water) is mixed with the reactant gas (for example, hydrogen or air) supplied to the fuel cell, with a humidifier or the like. Moreover, since reaction-generated water is produced by the electrochemical reaction when the fuel cell is in operation, the fuel cell exhaust gas, particularly the exhaust gas from oxygen electrode, is a high-humidity gas.
Therefore, in the protective apparatus of the fuel cell according to one example of the aforementioned conventional technology, due to the highly humid off-gas discharged from the fuel cell, condensation may occur on the hydrogen detector and the like, positioned in the flow path of the off-gas. In this case, deterioration of, and damage to, the hydrogen detector may occur. In particular, in the solid high-polymer membrane-type fuel cell, the normal operating temperature is lower than the evaporation temperature of water, so that the off-gas is highly humid and a gas having a high water content is discharged. Therefore there is the problem that the moisture content of the off-gas readily condenses.
Furthermore, for example, when the gas-contact combustion-type hydrogen detector is provided, particularly when provided in the exhaust system on the oxygen electrode side of the fuel cell, if electricity is supplied to the gas detection element while humidifying water or reaction-generated water and the like is adhered to it, localized non-uniformities in temperature distribution occur on the surface of the element, and may result in damage to, and decreased sensitivity of, the element.